The process for device, such as light-emitting diode or DRAM, includes a photolithography process for patterning a variety of thin films. For the photolithography process, there are used a photoresist composition and photoresist patterns formed from the photoresist composition. There are two types of photoresist compositions: positive and negative.
The negative photoresist composition is a photoresist composition of which the unexposed portions are removed when a substrate or a target thin film undergoes photoresist coating, exposure and development. Such a negative photoresist composition is generally used for patterning metal films, such as electrodes, in fabrication of various devices, such as light-emitting diodes (LEDs) or liquid crystal devices (LCDs). More specifically, the use of the negative photoresist composition has been considered in the fabrication process for LCD thin film transistor substrate or in the lift-off process for forming LED electrodes.
The lift-off process refers to a method of creating patterns in which the negative photoresist composition is used to form a photoresist pattern with reverse taper profile, which is then used to pattern a target thin film, such as a metal film. However, the use of the conventional negative photoresist composition in forming photoresist patterns frequently fails to provide photoresist patterns with a reverse taper profile. In this case, when the target thin film, such as a metal film, is formed on the photoresist pattern, residuals of the target thin film (e.g., metal residuals) often accumulate on the sidewalls of the photoresist pattern. These residuals become a potential cause of a short circuit between electrodes formed from the metal film and end up with defects in the device.
Furthermore, the conventional negative photoresist composition exhibits sensitivity not high enough to achieve effective and good patterning of the target thin film, such as a metal film. Particularly, this problem becomes more prominent due to the recent tendencies in a variety of devices towards high integration and micronization.